Six fire engines and 35 firefighters and officers were called to a fire in a block of flats in Warner Close, Colindale.
Most of a flat on the second floor of the building was damaged by fire.
Around 20 people left the building before the arrival of the Brigade. A man and woman were led to safety by crews wearing breathing apparatus.
Six people suffered smoke inhalation and were taken to hospital by London Ambulance Service crews. A further three people were treated at the scene.
The Brigade was called at 1905 and the fire was under control at 2142. Fire crews from Hendon, Stanmore, West Hampstead, Willesden and Mill Hill fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.